1. Field of the Invention
The present invention relates to a roller retainer which is used in a direct-acting guide device, a roller screw, or the like, and in which a roller rolling in a circulation path is held so as to be rotatable/slidable.
2. Description of the Related Art
A roller screw having rollers interposed between a screw shaft and a nut member is known. When the screw shaft is rotated relative to the nut member, the nut member makes reciprocating motion in a direction of the axis of the screw shaft. The rollers make rolling motion so as to go around the outer circumference of a screw groove between the screw shaft and the nut member. Thus, the rollers circulate in a roller circulation path. A helical roller rolling groove is formed in the screw shaft. The roller circulation path containing a helical load rolling groove corresponding to the roller rolling groove is formed in the nut member. In the roller screw, the plurality of rollers maybe arranged in the roller circulation path so as to be parallel to one another to keep the axes of adjacent rollers approximately parallel to each other, or the plurality of rollers may be arranged in the roller circulation path so as to cross one another to intersect the axes of adjacent rollers.
Generally, in the case of a full-roller type roller screw in which only rollers are arranged in the roller circulation path, the respective rollers make no consistent motion so that each of the rollers falls down in a plane containing the axis of the roller and the direction of the movement of the roller to cause skew. Hence, the rollers are prevented from circulating while arranged in the roller circulation path. Though not relating to the roller screw, a belt-like ball retainer for rotatably/slidably holding a plurality of balls of a ball screw to make arranged circulation of the balls is known (for example, see JP-A-11-223258). The ball retainer holds the balls in the form of a linear chain so that front-side and rear-side adjacent balls can circulate smoothly.
On the other hand, a cage for holding corresponding one of rollers arranged and received in a circulation path of a direct-acting guide device is known (see JP-A-60-205013). FIG. 17 shows such cages circulating in the roller circulation path of the direct-acting guide device. A plurality of rollers 1 are cross-arranged in the roller circulation path 2 so that the axes of adjacent rollers 1 cross each other. The direction of the rollers 1 is changed two-dimensionally in between a linear load passage 2a and a U-shaped changing-direction passage 2b. FIG. 18 is a front view of a cage 3 with a roller 1 when viewed in the direction of the movement thereof. FIG. 19 is a sectional view taken along the line Axe2x80x94A in FIG. 18. Because of the cross arrangement of the rollers 1, the roller circulation path 2 is shaped substantially like a square in section. The cages 3 rotatably/slidably hold the rollers 1 in container holes 3a of the cages 3 individually and correspondingly while the outer circumferences 1a of the rollers 1 are exposed partially slightly. The thickness of the cage 3 (the radial thickness of the roller) is set to be approximately equal to that of the roller 1. As shown in the drawings, the shape of the cage 3 viewed from the front side in the direction of the movement forms a square approximately equal to the sectional shape of the roller circulation path 2 so that the roller 1 can be guided by the cage 3. As shown in FIG. 17, two end surfaces 3a and 3b which form an angle of not smaller than 90xc2x0 are formed at two ends of the adjacent cages 3 in the direction of the movement thereof. When the cage 3 is located on the linear load passage 2a, one end surface 3a is positioned so as to be approximately perpendicular to the load passage 2a. When the cage 3 is located on the U-shaped changing-direction passage 2b, the other end surface 3b is directed to the direction of the radius of the changing-direction passage 2b. Thus, the cages 3 with the rollers 1 circulate in the roller circulation path 2 while the end surfaces 3a and 3b of adjacent cages 3 press each other.
In the background-art ball retainer holding balls in the form of a straight chain, however, the circulation path of the ball screw draws a spiral. Hence, the ball retainer is twisted so spirally that load is applied on the ball retainer. There is a risk that the ball retainer may be broken by the load.
On the other hand, the cages 3 by which the rollers 1 arranged and received in the roller circulation path 2 of the direct-acting guide device are held individually are adapted to the case where the linear load passage and the U-shaped changing-direction passage are positioned on one plane so that the direction of the rollers 1 is changed two-dimensionally. For example, in a circulation path of a roller screw, however, not two-dimensional direction changing but three-dimensional direction changing and, accordingly, twisting motion around the direction of the movement, may be required. In the aforementioned cages 3, the circulating cages 3 are not allowed to rotate slightly around the axes of the rollers 1 respectively so that the cages 3 can hardly make such complex motion. This is because the shape of each cage 3 is formed to be approximately equal to the sectional shape of the roller circulation path 2 and because adjacent cages 3 are in surface contact with each other at large-area flat end surfaces 3a and 3b. Moreover, a lubricant can hardly enter in between the cage 3 and a corresponding roller 1 because the circumference of the roller 1 except part of the outer circumference 1a is covered with the cage 3. Hence, the roller 1 cannot be lubricated sufficiently. Moreover, the approximately whole section of the roller circulation path 2 is covered with the cage 3. There is a problem that a support member for supporting the cage 3 to prevent the cage 3 from dropping down from the slide member when the slide member is removed from the race rail is hardly provided in the circulation path.
An object of the present invention has been made to solve the above object, and therefore an object of the invention is to provide a roller retainer which can circulate smoothly even in a complex kinetic condition such as a three-dimensional changing-direction passage and in which lubricating oil can be supplied sufficiently to rollers, and to provide a direct-acting guide device and a roller screw using such roller retainers.
The present invention will be described below. Although the reference numerals in the accompanying drawings are put in parentheses to make understanding of the present invention easy, the present invention is not limited to the embodiments based on the accompanying drawings.
To solve the problem, the inventor of the present invention provides a system in which rollers circulating in a circulating path are not held in the form of a straight chain but are held in roller retainers individually so that the rollers circulate in a circulation path while the rear-side roller retainer presses the front-side roller retainer. Further, because linear portions and curved portions mainly exit in the circulation path, the inventor considers the shape of each end of the roller retainer in a direction of the movement thereof so that pressing force is transmitted smoothly either in the linear portions or in the curved portions. Further, the inventor provides a system in which roller retainers can circulate while allowed to rotate slightly around the axes of the rollers respectively when the roller retainers circulate while pressing each other. Accordingly, the roller retainers can be adapted to a three-dimensionally complex circulation path on the assumption that the rollers are arranged in the circulation path and the axes of adjacent rollers are substantially kept parallel to each other.
Specifically, according to a first aspect of the present invention, there is provided a roller retainer assembly having roller retainers (15) for individually and correspondingly retaining a plurality of rollers (7) circulating in a roller circulation path inclusive of linear and curved races, wherein: each of the roller retainers (15) is made thin to hold opposite side surfaces of the roller (7) and front and rear surfaces of the roller (7) in a direction of movement of the roller (7); a linear guide portion (16a, 17a) and a curve guide portion (16b, 17b) which are different in inclination angle from each other are formed in opposite end surfaces of the roller retainer (15) in a direction of movement of the roller retainer (15); and the linear guide portion (16a, 17a) of the roller retainer (15) comes into contact with an adjacent roller retainer (15) in the linear race and the curve guide portion (16b, 17b) of the roller retainer (15) comes into contact with an adjacent roller retainer (15) in the curved race. By the provision of the roller retainer assembly, the above-mentioned problem is therefore solved. The thickness of the roller retainer (15) is selected to be not larger than 90%, preferably not larger than 60% of the roller diameter.
According to this invention, in either of linear races and curved races constituting a circulation race, adjacent roller retainers can press each other without spoiling the posture of a roller located in the front side in the direction of the movement of the roller. Hence, rollers can be aligned so that smooth circulation can be obtained. Further, because the roller retainer is made thin, the following effects are obtained.
(1) Adjacent roller retainers can press each other while they are allowed to rotate slightly around the axes of corresponding rollers respectively. As a result, the roller retainer can be obtained as a roller retainer adapted to a complex circulation path such as a three-dimensional changing-direction passage or a helical load rolling passage shaped like a screw.
(2) A large space can be secured for reserving lubricating oil in the circulation path. Hence, the rollers can be lubricated sufficiently.
(3) A drop-down prevention member for supporting the roller retainer can be provided in the circulation path so that the roller retainer is prevented from dropping down from the nut member, or the like.
According to a second aspect of the invention, there is provided a roller retainer assembly having roller retainers (31) for individually and correspondingly retaining a plurality of rollers (7) circulating in a roller circulation path inclusive of linear and curved races, wherein: each of the roller retainers (31) is made thin to hold the opposite side surfaces of the roller (7) and either one of front and rear surfaces of the roller (7) in a direction of movement of the roller (7); a linear guide portion (32a) and a curve guide portion (32b) which are different in inclination angle are formed in one end surface of the roller retainer (31) in a direction of movement of the roller retainer (31); and the linear guide portion (32a) of the roller retainer (31) comes into contact with an adjacent roller (7) in the linear race and the curve guide portion (32b) of the roller retainer (31) comes into contact with an adjacent roller (7) in the curved race. By the provision of the roller retainer assembly, the above-mentioned problem is therefore solved.
According to this invention, in addition to the same operation and effect as those of the aforementioned invention, the roller retainer holds either of front and rear surfaces of a corresponding roller in the direction of the movement of the roller. Hence, the space occupied by one roller retainer in the circulation path is reduced so that the number of rollers can be increased. Hence, the load capacity of a direct-acting guide device or roller screw using such roller retainers can be increased.
According to a third aspect of the invention, in the first aspect of the invention, each of the linear guide portion (16a, 17a) and the curve guide portion (16b, 17b) of the roller retainer (15) is formed to be a curved surface shaped like a circular arc in section so as to come into linear contact with the adjacent roller retainer (15).
According to this invention, adjacent roller retainers can press each other while they are securely allowed to rotate slightly around the axes of corresponding rollers respectively.
According to a fourth aspect of the invention, in the second aspect of the invention, each of the linear guide portion (32a) and the curve guide portion (32b) of the roller retainer (31) is formed to be a curved surface in accordance with an outer circumference of the roller (7).
According to this invention, a roller and a roller retainer which are adjacent to each other can press each other while the roller retainer is securely allowed to rotate slightly around the axis of a corresponding roller. Moreover, because the roller retainer comes into surface contact with a roller located in the front side or rear side in the direction of the movement of the roller retainer, contact surface pressure can be reduced.
According to a fifth aspect of the invention, in the roller retainer assembly as stated in the first or third aspect, a hinge protrusion (26) is provided at a point of intersection between the linear guide portion (16a) and the curve guide portion (16b) in one end surface of the roller retainer (25); and a hinge recess (27) is provided at a point of intersection between the linear guide portion (17a) and the curve guide portion (17b) in the other end surface of the roller retainer (25) so that the hinge recess (27) engages with the hinge protrusion (27) of an adjacent roller retainer.
According to this invention, the roller retainer is only allowed to swing around a hinge constituted by a combination of the hinge protrusion and the hinge recess in a plane containing the axis of a corresponding roller and the direction of the movement of the roller. Hence, the roller can be prevented from falling down even in a boundary shifting from a linear race to a curved race. Hence, smooth circulation of the roller can be ensured.
According to a sixth aspect of the invention, in any one of the first to fifth aspects, drop-down prevention protrusions (20) are formed on either one of the roller retainer (15) and the opposite side surfaces of the roller (7); and drop-down prevention recesses (21) are formed in the other one of the roller retainer and the opposite side surfaces of the roller so that the drop-down prevention protrusions are fitted into the drop-down prevention recesses.
According to this invention, the roller can be prevented from dropping out from the roller retainer. For example, even in the case where a slide member such as a nut member is removed from the race rail, the roller retainer can prevent the roller from dropping down from the slide member so that the roller can be prevented from dropping down from the slide member.
According to a seventh aspect of the invention, in any one of first to sixth aspects, a thickness of the roller retainer (15) is selected to be not smaller than 50% of a diameter of the roller. When a tapered roller is used as each of the rollers, the terminology xe2x80x9croller diameterxe2x80x9d used herein means the smallest roller diameter.
If the thickness of each of the roller retainers is smaller than 50% of the roller diameter, the front end of the succeeding roller retainer in the circulation path enters the gap between the front-side roller retainer and the roller rolling groove so that adjacent roller retainers overlap each other. As a result, there is a risk that the circulation of rollers may stop. When the thickness of each of the roller retainers is not smaller than 50% of the roller diameter, such adjacent roller retainers can be prevented from overlapping each other.
Further, according to the invention, there is also provided a direct-acting guide device comprising: a race shaft (41, 51) containing a roller rolling surface (41a, 51a); a slide member (42, 52) including a roller circulation path containing a load rolling surface (42a, 52a) corresponding to the roller rolling surface (41a, 51a), the slide member (42, 52) being fitted to the race shaft (41, 51) so as to be freely movable relative to the race shaft (41, 51); a plurality of rollers (43, 53) arranged and received in the roller circulation path so as to circulate in accordance with movement of the slide member (42, 52) relative to the race shaft (41, 51); and a plurality of roller retainers (15) for holding the plurality of rollers (43, 53) individually and correspondingly so that the plurality of rollers (43, 53) are rotatable/slidable, wherein: the plurality of rollers (43, 53) are arranged and received so that the axes of adjacent rollers (43, 53) are kept approximately parallel to each other; each of the roller retainers (15) is made thin to hold opposite side surfaces of corresponding one of the rollers (7) and front and rear surfaces of the roller (7) in a direction of movement of the roller (7); a linear guide portion (16a, 17a) and a curve guide portion (16b, 17b) which are different in inclination angle from each other are formed in each of opposite end surfaces of the roller retainer (15) in a direction of movement of the roller retainer (15); and the linear guide portion (16a, 17a) of the roller retainer (15) comes into contact with an adjacent roller retainer (15) in a linear race and the curve guide portion (16b, 17b) of the roller retainer (15) comes into contact with an adjacent roller retainer (15) in a curved race.
Further, according to the invention, there is also provided a direct-acting guide device comprising: a race shaft (41, 51) containing a roller rolling surface (41a, 51a); a slide member (42, 52) including a roller circulation path containing a load rolling surface (42a, 52a) corresponding to the roller rolling surface (41a, 51a), the slide member (42, 52) being fitted to the race shaft (41, 51) so as to be freely movable relative to the race shaft (41, 51); a plurality of rollers (43, 53) arranged and received in the roller circulation path so as to circulate in accordance with movement of the slide member (42, 52) relative to the race shaft (41, 51); and a plurality of roller retainers (15) for holding the plurality of rollers (43, 53) individually and correspondingly so that the plurality of rollers (43, 53) are rotatable/slidable, wherein: the plurality of rollers (43, 53) are arranged and received so that the axes of adjacent rollers (43, 53) are kept approximately parallel to each other; each of the roller retainers (31) is made thin to hold opposite side surfaces of corresponding one of the rollers (7) and either one of front and rear surfaces of the roller (7) in a direction of movement of the roller (7); a linear guide portion (32a) and a curve guide portion (32b) which are different in inclination angle are formed in one end surface of the roller retainer (31) in a direction of movement of the roller retainer (31); and the linear guide portion (32a) of the roller retainer (31) comes into contact with an adjacent roller (7) in a linear race and the curve guide portion (32b) of the roller retainer (31) comes into contact with an adjacent roller (7) in a curved race.
Further, according to the invention, there is also provided a roller screw comprising: a race shaft (5) containing a helical roller rolling surface (5a); a slide member (6) including a roller circulation path (8) containing a helical load rolling surface (6a) corresponding to the roller rolling surface (5a), the slide member (6) being fitted to the race shaft (5) so as to be freely movable relative to the race shaft (5); a plurality of rollers (7) arranged and received in the roller circulation path (8) so as to circulate in accordance with movement of the slide member (6) relative to the race shaft (5); and a plurality of roller retainers (15) for holding the plurality of rollers (7) individually and correspondingly so that the plurality of rollers (7) are rotatable/slidable, wherein: the plurality of rollers (7) are arranged and received so that axes of adjacent rollers (7) are kept approximately parallel to each other; each of the roller retainers (15) is made thin to hold opposite side surfaces of corresponding one of the rollers (7) and front and rear surfaces of the roller (7) in a direction of movement of the roller (7); a linear guide portion (16a, 17a) and a curve guide portion (16b, 17b) which are different in inclination angle from each other are formed in each of opposite end surfaces of the roller retainer (15) in a direction of movement of the roller retainer (15); and the linear guide portion (16a, 17a) of the roller retainer (15) comes into contact with an adjacent roller retainer (15) in a linear race and the curve guide portion (16b, 17b) of the roller retainer (15) comes into contact with an adjacent roller retainer (15) in a curved race.
Further, according to the invention, there is also provided a roller screw comprising: a race shaft (5) containing a helical roller rolling surface (5a); a slide member (6) including a roller circulation path (8) containing a helical load rolling surface (6a) corresponding to the roller rolling surface (5a), the slide member (6) being fitted to the race shaft (5) so as to be freely movable relative to the race shaft (5); a plurality of rollers (7) arranged and received in the roller circulation path (8) so as to circulate in accordance with movement of the slide member (6) relative to the race shaft (5); and a plurality of roller retainers (15) for holding the plurality of rollers (7) individually and correspondingly so that the plurality of rollers (7) are rotatable/slidable, wherein: the plurality of rollers (7) are arranged and received so that axes of adjacent rollers (7) are kept approximately parallel to each other; each of the roller retainers (31) is made thin to hold opposite side surfaces of corresponding one of the rollers (7) and either one of front and rear surfaces of the roller (7) in a direction of movement of the roller (7); a linear guide portion (32a) and a curve guide portion (32b) which are different in inclination angle are formed in one end surface of the roller retainer (31) in a direction of movement of the roller retainer (31); and the linear guide portion (32a) of the roller retainer (31) comes into contact with an adjacent roller (7) in a linear race and the curve guide portion (32b) of the roller retainer (31) comes into contact with an adjacent roller (7) in a curved race.